If you're sick of Firefox 2 eating up over a gigabyte of memory only to freeze up and crash, it may be time to move onto Firefox 3. The new version of our favorite browser has seen its fifth and final beta release, and Mozilla says its for testing purposes only. However, the Firefox 3 beta is leaner, meaner, faster, and just plain better than Firefox 2—and don't tell Daddy Mozilla, but even at this early stage, we've found it to be stable enough for full-time use. There are a few ways you can start using Firefox 3 without blowing your browser setup to hell or losing your most important extensions. Here's how.

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Why Firefox 3 Now

Firefox 3 is in a late-stage beta, which means bugs are still getting reported and features are still getting finalized. Its next iteration will be a feature-complete release candidate, with the final public release due out in June. You can play it safe and wait till June, of course. However, Firefox 3 is chock full of new features that are reason enough to test-drive it—like a smarter address bar, better bookmarks, more native look for Mac, Windows, and Linux.

But the most compelling reason not only to try it out but to switch to Firefox 3 for regular browsing now? Significantly improved memory management and much-reduced risk of crashes. Firefox 3 just doesn't hog all your RAM, seize your computer, and flip out with the spectacular regularity of Firefox 2. Plus it's just plain faster dealing with the web pages it opens while it's not crashing. If that's enough to convince you, read on for how to get into the beta without hosing your beloved browser setup.

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Windows: Play It Safe with Self-Contained Portable Firefox 3

If you want to use Firefox 3 without losing Firefox 2 or touching its settings, you want the portable Firefox 3 beta application. This standalone, self-contained version of Firefox isn't just for thumb drives. Save it to any folder on your computer (I prefer one called Firefox 3b5 on my desktop) and it creates a whole new user profile and runs completely separate from Firefox 2. One catch: you can't run Firefox 2 and portable Firefox 3 at the same time.

When you run Firefox 3 portable you'll start out with a fresh profile that doesn't have your extensions, bookmarks, and homepage set. Instead of going through all the work of setting those up again, you can copy your Firefox 2 user settings to Firefox 3 portable. Here's how.

First, make sure NO versions of Firefox are running at all, but that you've run Firefox 3 portable at least once.

Navigate to the Firefox 2 profile folder you want to copy to Firefox 3. (Here's where to find it; most likely it will have the word "default" in the folder name.)

Copy that entire folder and paste it into the Your-Firefox3-Folder/Data/ folder.

Go Whole Hog (With a Backup)

If you're feeling really courageous, you can just wipe out Firefox 2 entirely and dive into Firefox 3 full-time, like I did. This means Firefox 3 will take over your existing Firefox profile. While I haven't seen problems with this on Windows or Mac, backups are always good insurance. So just to be safe: back up your Firefox profile, just in case you need to revert to Firefox 2 at some point in the future. (Note: MozBackup is for Windows only. Mac users can back up their profile manually by making a copy of their user profile folder.)

Make Your Extensions Work with the Firefox 3 Beta

Now that you're running Firefox 3 the first thing it'll tell you is that your extensions aren't compatible with the new version. Don't panic. It's true that many Firefox extension developers haven't updated their add-ons to work with Firefox 3. But in many instances, this is just a matter of the extension reporting back to the application that it isn't yet compatible, even though the add-on might work anyway. Instead of waiting for your favorite extensions to get updated, you can tell Firefox to enable them no matter what.

There are two ways to do this:

Download the Nightly Tester Tools extension. Once it's installed and you've restarted, your Firefox 3 Add-ons dialog will have a "Make all compatible" button, as pictured. Press that puppy to make your extensions work with Firefox 3 (after a restart, that is).

Note that you may still get a message about extensions that don't "provide secure updates" even after hitting this button. Use about:config as detailed below for a workaround to the secure updates issue.

Finally, once you're happily using Firefox 3 (beta 5 and beyond), type about:robots in the address bar to see a few fun messages from our robot overlords, ya big geek.

Are you a Firefox 3 convert? What's your testing experience been like? Let us know in the comments.

Gina Trapani, the editor of Lifehacker, is in love with Firefox 3 even in its fetal stage. Her weekly feature, Geek to Live, appears every Monday on Lifehacker. Subscribe to the Geek to Live feed to get new installments in your newsreader.